Biological basis of behavior: Nervous system
Hemispheric differences and hemispheric dominance
- [Voiceover] Here I have something that looks like a picture of two different brains, but I actually want you to think about it as two halves of the same brain. So imagine, if you will, that I drew a line down the center of someone's head, and then split their brain down the middle. In both cases, this side would be the front of the brain, and this would be the back, and this would be the top, and here would be the bottom. And let's say that this person was looking at you when we peeled their brain in two. In that case, this would be their left side of their brain, and this would be their right side. The first thing you might notice, looking at this brain, is that the sides are basically identical. And that is absolutely correct. For the most part, the two sides look physically identical to one another. But even though they look identical, for a great majority of people, the two sides of the brain actually do different things. And we're gonna talk a little bit about that. The first thing that I wanna talk about is contralateral control. And what that means, for the most part, is that the left side of the brain controls the right side of the body, and vice versa. So the right side of the brain controls the left side of the body. And this is true for basically all of your senses. So information from your left visual field goes to the right side of your occipital cortex, the motor neurons on the right side of your brain control the left side of your body. The only thing that I can immediately think of that this doesn't apply to is smell. So in that case, the two cerebral hemispheres communicate with the same side of the body. In other words, they communicate ipsilaterally instead of contralaterally. Another interesting thing to note is that we actually have a dominant hemisphere. Meaning that we also have a nondominant one. And because we know that the brain communicates contralaterally with the body, the dominant hemisphere is typically the one that's opposite of the hand that we write with. So people who are right-handed have a tendency to be left-brained, and vice versa. But because being right-handed is so dominant, this means that the left hemisphere is the dominant hemisphere for the vast majority of people. Although handedness is the easiest way to identify our dominant hemisphere, the dominant hemisphere is actually responsible for a lot more than that. One thing that we find in the dominant hemisphere, which is typically the left hemisphere, is language. Specifically, an area called Broca's area, which is responsible for speech production, and Wernicke's area, which is responsible for comprehension, are both located in the dominant hemisphere. There's also been some research that shows that the dominant hemisphere is analytic in nature. That along with language, things like logic and math skills are also both mainly controlled by the dominant hemisphere. The nondominant hemisphere, typically the right hemisphere, has a less prominent role in language, but it is responsible for many other tasks. For example, the nondominant hemisphere plays an important role in understanding the emotional tone of language. And it allows us to recognize whether the people that we're speaking to are happy or depressed or anxious, just by the way that they sound. So while the nondominant hemisphere may not control language in the way that the dominant hemisphere does, it still plays an important role. Research has also implicated that the non dominant hemisphere may play an important role in things like creativity, and music, and spatial processing. There's also been some evidence that shows that the nondominant hemisphere helps us pull together big-picture concepts. I do want to take a moment to note, before we go any further, that it's really easy to get carried away with this left brain, right brain thing. I've seen a lot of things on the internet that say, "Hey, take this quiz and it'll show you "if you're left-brained or right-brained," and it doesn't really work like that. The vast majority of people have a dominant and a nondominant hemisphere, and we use both of them. There's not really a way to tap in to one over the other, so you need to be really careful in how you interpret this information. One last thing you might be wondering about is that if we have two different cerebral hemispheres, how do they talk to one another? How do they communicate? And the answer is that they communicate through a large band of fibers, known as the corpus callosum. And without this corpus callosum, the two sides of the brain can't communicate with one another. Each one doesn't know what the other one is doing. And that can produce some incredibly interesting consequences that we're going to talk about in a future video.